Perchloric Acid, an Effective Catalyst for Thermosetting Self‐Crosslinking Hydroxy Acrylic Resins

ABSTRACT Ethyl acrylate (EA)–2‐hydroxyethyl acrylate (HEA) and ethyl acrylate (EA)–4‐hydroxybutyl acrylate (HBA) containing acrylic resins were crosslinked by the action of perchloric acid. The crosslinking is based on the intermediate formation of alkyl perchlorate esters from the hydroxyl entities. Thin films of the resins were obtained from ethanol solutions mixed with catalytic or stoichiometric amounts of perchloric acid relative to the hydroxy entity. They could be cured between 85°C and 135°C. Ethyl perchlorate was found to evaporate from the resins during the curing phase. The additional liberation of tetrahydrofuran was found in HBA derivatives (by TGA/MS). 13 C CP MAS NMR analysis revealed that HEA copolymers dominantly form ether crosslinks when low amounts of perchloric acid are used, and ethylene diester crosslinks when using stoichiometric amounts. HBA copolymers dominantly form butylene diester crosslinks irrespective of the amount of perchloric acid. Various amounts of carboxylic acid entities appear as the result of ester hydrolysis. High amounts of perchloric acid with a fast crosslinking lead to resins with a glass temperature of 50°C–53°C; lower amounts give resins with a glass temperature as low as −10°C.